Why does the density of a substance remain the same for different amounts of the substance?

Margaret wants to make an orange flavored drink by stirring powdered drink mix into a glass of water. she doesn't like drinks that have small clumps of powdered solid in them, so she wants the drink to be a perfect solution. what factors should margaret not consider when deciding how much powder to add to her glass of water?

When balancing a chemical equation:

If you burn 46.6 g of hydrogen and produce 416 g of water, how much oxygen reacted